The present invention is directed to new and useful improvements in rotary vacuum drum filters and more particularly to filtrate drainage compartments for such filters.
Rotary drum vacuum filters are well known and are used for many industrial processes, for example, in the pulp and paper industry to filter and wash pulp slurries. These filters comprise a cylindrical drum mounted for rotation in a tank containing a slurry solution. A filter media is provided about the drum and filtrate is drawn into filtrate compartments beneath the filter media when vacuum is applied thereto from within the drum.
In one such type filter the drum has a wire wound deck which provides a support for the filter media which may, for example, be a wire mesh or permeable cloth material. The deck wire is wound tightly about the drum across a plurality of spaced and parallel longitudinal ribs or divider strips which are spaced equally distant one from the other along the periphery of the cylindrical drum. The areas between each pair of adjacent dividers constitute longitudinally extending filtrate drainage compartments.
When the drum is rotated through a filtration cycle a vacuum is maintained inside the drum as the drum ascends from the tank. A filter cake is thereby formed on the surface of the filter media and filtrate is drawn into the filtrate compartments by the vacuum and fed to an appropriate discharge opening in the drum. As the drum descends into the tank the vacuum is interrupted by appropriate valve means and the filter cake is removed from the surface of the filter media by a suitable doctoring means.
A problem is encountered in filters of this general type in the processing of certain slurries in providing means to prevent rewetting of the dried filter cake on the filter media from a runback of the filtrate from the filtrate compartments to the cake as the drum rotates in the descending path into the tank when the vacuum to the filtrate compartments is interrupted.
It is an object of the present invention to provide novel means for containing the filtrate in the filtrate compartments of a rotary vacuum drum filter.
Another object is to provide novel means for retrofitting existing filters with filtrate runback prevention means.
Still another object is to provide a simple and effective replaceable baffle means for preventing run-back of filtrate in the filter cake in the filtration cycle of a drum filter.